2 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.5//EN"
3 "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
4 <!ENTITY % entities SYSTEM
"custom-entities.ent" >
7 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
9 <refentry id=
"systemd-nspawn"
10 xmlns:
xi=
"http://www.w3.org/2001/XInclude">
13 <title>systemd-nspawn
</title>
14 <productname>systemd
</productname>
18 <refentrytitle>systemd-nspawn
</refentrytitle>
19 <manvolnum>1</manvolnum>
23 <refname>systemd-nspawn
</refname>
24 <refpurpose>Spawn a command or OS in a light-weight container
</refpurpose>
29 <command>systemd-nspawn
</command>
30 <arg choice=
"opt" rep=
"repeat">OPTIONS
</arg>
31 <arg choice=
"opt"><replaceable>COMMAND
</replaceable>
32 <arg choice=
"opt" rep=
"repeat">ARGS
</arg>
36 <command>systemd-nspawn
</command>
37 <arg choice=
"plain">--boot
</arg>
38 <arg choice=
"opt" rep=
"repeat">OPTIONS
</arg>
39 <arg choice=
"opt" rep=
"repeat">ARGS
</arg>
44 <title>Description
</title>
46 <para><command>systemd-nspawn
</command> may be used to run a command or OS in a light-weight namespace
47 container. In many ways it is similar to
<citerefentry
48 project='man-pages'
><refentrytitle>chroot
</refentrytitle><manvolnum>1</manvolnum></citerefentry>, but more powerful
49 since it fully virtualizes the file system hierarchy, as well as the process tree, the various IPC subsystems and
50 the host and domain name.
</para>
52 <para><command>systemd-nspawn
</command> may be invoked on any directory tree containing an operating system tree,
53 using the
<option>--directory=
</option> command line option. By using the
<option>--machine=
</option> option an OS
54 tree is automatically searched for in a couple of locations, most importantly in
55 <filename>/var/lib/machines/
</filename>, the suggested directory to place OS container images installed on the
58 <para>In contrast to
<citerefentry
59 project='man-pages'
><refentrytitle>chroot
</refentrytitle><manvolnum>1</manvolnum></citerefentry> <command>systemd-nspawn
</command>
60 may be used to boot full Linux-based operating systems in a container.
</para>
62 <para><command>systemd-nspawn
</command> limits access to various kernel interfaces in the container to read-only,
63 such as
<filename>/sys/
</filename>,
<filename>/proc/sys/
</filename> or
<filename>/sys/fs/selinux/
</filename>. The
64 host's network interfaces and the system clock may not be changed from within the container. Device nodes may not
65 be created. The host system cannot be rebooted and kernel modules may not be loaded from within the
68 <para>Use a tool like
<citerefentry
69 project='mankier'
><refentrytitle>dnf
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry
70 project='die-net'
><refentrytitle>debootstrap
</refentrytitle><manvolnum>8</manvolnum></citerefentry>, or
71 <citerefentry project='archlinux'
><refentrytitle>pacman
</refentrytitle><manvolnum>8</manvolnum></citerefentry> to
72 set up an OS directory tree suitable as file system hierarchy for
<command>systemd-nspawn
</command> containers. See
73 the Examples section below for details on suitable invocation of these commands.
</para>
75 <para>As a safety check
<command>systemd-nspawn
</command> will verify the existence of
76 <filename>/usr/lib/os-release
</filename> or
<filename>/etc/os-release
</filename> in the container tree before
77 booting a container (see
78 <citerefentry><refentrytitle>os-release
</refentrytitle><manvolnum>5</manvolnum></citerefentry>). It might be
79 necessary to add this file to the container tree manually if the OS of the container is too old to contain this
80 file out-of-the-box.
</para>
82 <para><command>systemd-nspawn
</command> may be invoked directly from the interactive command line or run as system
83 service in the background. In this mode each container instance runs as its own service instance; a default
84 template unit file
<filename>systemd-nspawn@.service
</filename> is provided to make this easy, taking the container
85 name as instance identifier. Note that different default options apply when
<command>systemd-nspawn
</command> is
86 invoked by the template unit file than interactively on the command line. Most importantly the template unit file
87 makes use of the
<option>--boot
</option> option which is not the default in case
<command>systemd-nspawn
</command>
88 is invoked from the interactive command line. Further differences with the defaults are documented along with the
89 various supported options below.
</para>
91 <para>The
<citerefentry><refentrytitle>machinectl
</refentrytitle><manvolnum>1</manvolnum></citerefentry> tool may
92 be used to execute a number of operations on containers. In particular it provides easy-to-use commands to run
93 containers as system services using the
<filename>systemd-nspawn@.service
</filename> template unit
96 <para>Along with each container a settings file with the
<filename>.nspawn
</filename> suffix may exist, containing
97 additional settings to apply when running the container. See
98 <citerefentry><refentrytitle>systemd.nspawn
</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
99 details. Settings files override the default options used by the
<filename>systemd-nspawn@.service
</filename>
100 template unit file, making it usually unnecessary to alter this template file directly.
</para>
102 <para>Note that
<command>systemd-nspawn
</command> will mount file systems private to the container to
103 <filename>/dev/
</filename>,
<filename>/run/
</filename> and similar. These will not be visible outside of the
104 container, and their contents will be lost when the container exits.
</para>
106 <para>Note that running two
<command>systemd-nspawn
</command> containers from the same directory tree will not make
107 processes in them see each other. The PID namespace separation of the two containers is complete and the containers
108 will share very few runtime objects except for the underlying file system. Rather use
109 <citerefentry><refentrytitle>machinectl
</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
110 <command>login
</command> or
<command>shell
</command> commands to request an additional login session in a running
113 <para><command>systemd-nspawn
</command> implements the
<ulink
114 url=
"https://systemd.io/CONTAINER_INTERFACE">Container Interface
</ulink> specification.
</para>
116 <para>While running, containers invoked with
<command>systemd-nspawn
</command> are registered with the
117 <citerefentry><refentrytitle>systemd-machined
</refentrytitle><manvolnum>8</manvolnum></citerefentry> service that
118 keeps track of running containers, and provides programming interfaces to interact with them.
</para>
122 <title>Options
</title>
124 <para>If option
<option>--boot
</option> is specified, the arguments
125 are used as arguments for the init program. Otherwise,
126 <replaceable>COMMAND
</replaceable> specifies the program to launch
127 in the container, and the remaining arguments are used as
128 arguments for this program. If
<option>--boot
</option> is not used and
129 no arguments are specified, a shell is launched in the
132 <para>The following options are understood:
</para>
137 <term><option>-q
</option></term>
138 <term><option>--quiet
</option></term>
140 <listitem><para>Turns off any status output by the tool
141 itself. When this switch is used, the only output from nspawn
142 will be the console output of the container OS
145 <xi:include href=
"version-info.xml" xpointer=
"v209"/></listitem>
149 <term><option>--settings=
</option><replaceable>MODE
</replaceable></term>
151 <listitem><para>Controls whether
152 <command>systemd-nspawn
</command> shall search for and use
153 additional per-container settings from
154 <filename>.nspawn
</filename> files. Takes a boolean or the
155 special values
<option>override
</option> or
156 <option>trusted
</option>.
</para>
158 <para>If enabled (the default), a settings file named after the
159 machine (as specified with the
<option>--machine=
</option>
160 setting, or derived from the directory or image file name)
161 with the suffix
<filename>.nspawn
</filename> is searched in
162 <filename>/etc/systemd/nspawn/
</filename> and
163 <filename>/run/systemd/nspawn/
</filename>. If it is found
164 there, its settings are read and used. If it is not found
165 there, it is subsequently searched in the same directory as the
166 image file or in the immediate parent of the root directory of
167 the container. In this case, if the file is found, its settings
168 will be also read and used, but potentially unsafe settings
169 are ignored. Note that in both these cases, settings on the
170 command line take precedence over the corresponding settings
171 from loaded
<filename>.nspawn
</filename> files, if both are
172 specified. Unsafe settings are considered all settings that
173 elevate the container's privileges or grant access to
174 additional resources such as files or directories of the
175 host. For details about the format and contents of
176 <filename>.nspawn
</filename> files, consult
177 <citerefentry><refentrytitle>systemd.nspawn
</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para>
179 <para>If this option is set to
<option>override
</option>, the
180 file is searched, read and used the same way, however, the order of
181 precedence is reversed: settings read from the
182 <filename>.nspawn
</filename> file will take precedence over
183 the corresponding command line options, if both are
186 <para>If this option is set to
<option>trusted
</option>, the
187 file is searched, read and used the same way, but regardless
188 of being found in
<filename>/etc/systemd/nspawn/
</filename>,
189 <filename>/run/systemd/nspawn/
</filename> or next to the image
190 file or container root directory, all settings will take
191 effect, however, command line arguments still take precedence
192 over corresponding settings.
</para>
194 <para>If disabled, no
<filename>.nspawn
</filename> file is read
195 and no settings except the ones on the command line are in
198 <xi:include href=
"version-info.xml" xpointer=
"v226"/></listitem>
204 <title>Image Options
</title>
209 <term><option>-D
</option></term>
210 <term><option>--directory=
</option></term>
212 <listitem><para>Directory to use as file system root for the container.
</para>
214 <para>If neither
<option>--directory=
</option>, nor
<option>--image=
</option> is specified the
215 directory is determined by searching for a directory named the same as the machine name specified
216 with
<option>--machine=
</option>. See
217 <citerefentry><refentrytitle>machinectl
</refentrytitle><manvolnum>1</manvolnum></citerefentry>
218 section
"Files and Directories" for the precise search path.
</para>
220 <para>In place of the directory path a
<literal>.v/
</literal> versioned directory may be specified, see
221 <citerefentry><refentrytitle>systemd.v
</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
224 <para>If neither
<option>--directory=
</option>,
<option>--image=
</option>, nor
225 <option>--machine=
</option> are specified, the current directory will be used. May not be specified
226 together with
<option>--image=
</option>.
</para></listitem>
230 <term><option>--template=
</option></term>
232 <listitem><para>Directory or
<literal>btrfs
</literal> subvolume to use as template for the
233 container's root directory. If this is specified and the container's root directory (as configured by
234 <option>--directory=
</option>) does not yet exist it is created as
<literal>btrfs
</literal> snapshot
235 (if supported) or plain directory (otherwise) and populated from this template tree. Ideally, the
236 specified template path refers to the root of a
<literal>btrfs
</literal> subvolume, in which case a
237 simple copy-on-write snapshot is taken, and populating the root directory is instant. If the
238 specified template path does not refer to the root of a
<literal>btrfs
</literal> subvolume (or not
239 even to a
<literal>btrfs
</literal> file system at all), the tree is copied (though possibly in a
240 'reflink' copy-on-write scheme — if the file system supports that), which can be substantially more
241 time-consuming. Note that the snapshot taken is of the specified directory or subvolume, including
242 all subdirectories and subvolumes below it, but excluding any sub-mounts. May not be specified
243 together with
<option>--image=
</option> or
<option>--ephemeral
</option>.
</para>
245 <para>Note that this switch leaves hostname, machine ID and
246 all other settings that could identify the instance
249 <xi:include href=
"version-info.xml" xpointer=
"v219"/></listitem>
253 <term><option>-x
</option></term>
254 <term><option>--ephemeral
</option></term>
256 <listitem><para>If specified, the container is run with a temporary snapshot of its file system that is removed
257 immediately when the container terminates. May not be specified together with
258 <option>--template=
</option>.
</para>
259 <para>Note that this switch leaves hostname, machine ID and all other settings that could identify
260 the instance unmodified. Please note that — as with
<option>--template=
</option> — taking the
261 temporary snapshot is more efficient on file systems that support subvolume snapshots or 'reflinks'
262 natively (
<literal>btrfs
</literal> or new
<literal>xfs
</literal>) than on more traditional file
263 systems that do not (
<literal>ext4
</literal>). Note that the snapshot taken is of the specified
264 directory or subvolume, including all subdirectories and subvolumes below it, but excluding any
267 <para>With this option no modifications of the container image are retained. Use
268 <option>--volatile=
</option> (described below) for other mechanisms to restrict persistency of
269 container images during runtime.
</para>
271 <xi:include href=
"version-info.xml" xpointer=
"v219"/>
276 <term><option>-i
</option></term>
277 <term><option>--image=
</option></term>
279 <listitem><para>Disk image to mount the root directory for the
280 container from. Takes a path to a regular file or to a block
281 device node. The file or block device must contain
285 <listitem><para>An MBR partition table with a single
286 partition of type
0x83 that is marked
287 bootable.
</para></listitem>
289 <listitem><para>A GUID partition table (GPT) with a single
291 0fc63daf-
8483-
4772-
8e79-
3d69d8477de4.
</para></listitem>
293 <listitem><para>A GUID partition table (GPT) with a marked
294 root partition which is mounted as the root directory of the
295 container. Optionally, GPT images may contain a home and/or
296 a server data partition which are mounted to the appropriate
297 places in the container. All these partitions must be
298 identified by the partition types defined by the
<ulink
299 url=
"https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable
300 Partitions Specification
</ulink>.
</para></listitem>
302 <listitem><para>No partition table, and a single file system spanning the whole image.
</para></listitem>
305 <para>On GPT images, if an EFI System Partition (ESP) is discovered, it is automatically mounted to
306 <filename>/efi
</filename> (or
<filename>/boot
</filename> as fallback) in case a directory by this name exists
309 <para>Partitions encrypted with LUKS are automatically decrypted. Also, on GPT images dm-verity data integrity
310 hash partitions are set up if the root hash for them is specified using the
<option>--root-hash=
</option>
313 <para>Single file system images (i.e. file systems without a surrounding partition table) can be opened using
314 dm-verity if the integrity data is passed using the
<option>--root-hash=
</option> and
315 <option>--verity-data=
</option> (and optionally
<option>--root-hash-sig=
</option>) options.
</para>
317 <para>Any other partitions, such as foreign partitions or swap partitions are not mounted. May not be specified
318 together with
<option>--directory=
</option>,
<option>--template=
</option>.
</para>
320 <para>In place of the image path a
<literal>.v/
</literal> versioned directory may be specified, see
321 <citerefentry><refentrytitle>systemd.v
</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
324 <xi:include href=
"version-info.xml" xpointer=
"v211"/></listitem>
328 <term><option>--image-policy=
<replaceable>policy
</replaceable></option></term>
330 <listitem><para>Takes an image policy string as argument, as per
331 <citerefentry><refentrytitle>systemd.image-policy
</refentrytitle><manvolnum>7</manvolnum></citerefentry>. The
332 policy is enforced when operating on the disk image specified via
<option>--image=
</option>, see
333 above. If not specified defaults to
334 <literal>root=verity+signed+encrypted+unprotected+absent:usr=verity+signed+encrypted+unprotected+absent:home=encrypted+unprotected+absent:srv=encrypted+unprotected+absent:esp=unprotected+absent:xbootldr=unprotected+absent:tmp=encrypted+unprotected+absent:var=encrypted+unprotected+absent
</literal>,
335 i.e. all recognized file systems in the image are used, but not the swap partition.
</para>
337 <xi:include href=
"version-info.xml" xpointer=
"v254"/></listitem>
341 <term><option>--oci-bundle=
</option></term>
343 <listitem><para>Takes the path to an OCI runtime bundle to invoke, as specified in the
<ulink
344 url=
"https://github.com/opencontainers/runtime-spec/blob/master/spec.md">OCI Runtime Specification
</ulink>. In
345 this case no
<filename>.nspawn
</filename> file is loaded, and the root directory and various settings are read
346 from the OCI runtime JSON data (but data passed on the command line takes precedence).
</para>
348 <xi:include href=
"version-info.xml" xpointer=
"v242"/></listitem>
352 <term><option>--read-only
</option></term>
354 <listitem><para>Mount the container's root file system (and any other file systems container in the container
355 image) read-only. This has no effect on additional mounts made with
<option>--bind=
</option>,
356 <option>--tmpfs=
</option> and similar options. This mode is implied if the container image file or directory is
357 marked read-only itself. It is also implied if
<option>--volatile=
</option> is used. In this case the container
358 image on disk is strictly read-only, while changes are permitted but kept non-persistently in memory only. For
359 further details, see below.
</para></listitem>
363 <term><option>--volatile
</option></term>
364 <term><option>--volatile=
</option><replaceable>MODE
</replaceable></term>
366 <listitem><para>Boots the container in volatile mode. When no mode parameter is passed or when mode is
367 specified as
<option>yes
</option>, full volatile mode is enabled. This means the root directory is mounted as a
368 mostly unpopulated
<literal>tmpfs
</literal> instance, and
<filename>/usr/
</filename> from the OS tree is
369 mounted into it in read-only mode (the system thus starts up with read-only OS image, but pristine state and
370 configuration, any changes are lost on shutdown). When the mode parameter is specified as
371 <option>state
</option>, the OS tree is mounted read-only, but
<filename>/var/
</filename> is mounted as a
372 writable
<literal>tmpfs
</literal> instance into it (the system thus starts up with read-only OS resources and
373 configuration, but pristine state, and any changes to the latter are lost on shutdown). When the mode parameter
374 is specified as
<option>overlay
</option> the read-only root file system is combined with a writable
375 <filename>tmpfs
</filename> instance through
<literal>overlayfs
</literal>, so that it appears at it normally
376 would, but any changes are applied to the temporary file system only and lost when the container is
377 terminated. When the mode parameter is specified as
<option>no
</option> (the default), the whole OS tree is
378 made available writable (unless
<option>--read-only
</option> is specified, see above).
</para>
380 <para>Note that if one of the volatile modes is chosen, its effect is limited to the root file system
381 (or
<filename>/var/
</filename> in case of
<option>state
</option>), and any other mounts placed in the
382 hierarchy are unaffected — regardless if they are established automatically (e.g. the EFI system
383 partition that might be mounted to
<filename>/efi/
</filename> or
<filename>/boot/
</filename>) or
384 explicitly (e.g. through an additional command line option such as
<option>--bind=
</option>, see
385 below). This means, even if
<option>--volatile=overlay
</option> is used changes to
386 <filename>/efi/
</filename> or
<filename>/boot/
</filename> are prohibited in case such a partition
387 exists in the container image operated on, and even if
<option>--volatile=state
</option> is used the
388 hypothetical file
<filename index=
"false">/etc/foobar
</filename> is potentially writable if
389 <option>--bind=/etc/foobar
</option> if used to mount it from outside the read-only container
390 <filename>/etc/
</filename> directory.
</para>
392 <para>The
<option>--ephemeral
</option> option is closely related to this setting, and provides similar
393 behaviour by making a temporary, ephemeral copy of the whole OS image and executing that. For further details,
396 <para>The
<option>--tmpfs=
</option> and
<option>--overlay=
</option> options provide similar functionality, but
397 for specific sub-directories of the OS image only. For details, see below.
</para>
399 <para>This option provides similar functionality for containers as the
<literal>systemd.volatile=
</literal>
400 kernel command line switch provides for host systems. See
401 <citerefentry><refentrytitle>kernel-command-line
</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
404 <para>Note that setting this option to
<option>yes
</option> or
<option>state
</option> will only work
405 correctly with operating systems in the container that can boot up with only
406 <filename>/usr/
</filename> mounted, and are able to automatically populate
<filename>/var/
</filename>
407 (and
<filename>/etc/
</filename> in case of
<literal>--volatile=yes
</literal>). Specifically, this
408 means that operating systems that follow the historic split of
<filename>/bin/
</filename> and
409 <filename>/lib/
</filename> (and related directories) from
<filename>/usr/
</filename> (i.e. where the
410 former are not symlinks into the latter) are not supported by
<literal>--volatile=yes
</literal> as
411 container payload. The
<option>overlay
</option> option does not require any particular preparations
412 in the OS, but do note that
<literal>overlayfs
</literal> behaviour differs from regular file systems
413 in a number of ways, and hence compatibility is limited.
</para>
415 <xi:include href=
"version-info.xml" xpointer=
"v216"/></listitem>
419 <term><option>--root-hash=
</option></term>
421 <listitem><para>Takes a data integrity (dm-verity) root hash specified in hexadecimal. This option enables data
422 integrity checks using dm-verity, if the used image contains the appropriate integrity data (see above). The
423 specified hash must match the root hash of integrity data, and is usually at least
256 bits (and hence
64
424 formatted hexadecimal characters) long (in case of SHA256 for example). If this option is not specified, but
425 the image file carries the
<literal>user.verity.roothash
</literal> extended file attribute (see
<citerefentry
426 project='man-pages'
><refentrytitle>xattr
</refentrytitle><manvolnum>7</manvolnum></citerefentry>), then the root
427 hash is read from it, also as formatted hexadecimal characters. If the extended file attribute is not found (or
428 is not supported by the underlying file system), but a file with the
<filename>.roothash
</filename> suffix is
429 found next to the image file, bearing otherwise the same name (except if the image has the
430 <filename>.raw
</filename> suffix, in which case the root hash file must not have it in its name), the root hash
431 is read from it and automatically used, also as formatted hexadecimal characters.
</para>
433 <para>Note that this configures the root hash for the root file system. Disk images may also contain
434 separate file systems for the
<filename>/usr/
</filename> hierarchy, which may be Verity protected as
435 well. The root hash for this protection may be configured via the
436 <literal>user.verity.usrhash
</literal> extended file attribute or via a
<filename>.usrhash
</filename>
437 file adjacent to the disk image, following the same format and logic as for the root hash for the
438 root file system described here. Note that there's currently no switch to configure the root hash for
439 the
<filename>/usr/
</filename> from the command line.
</para>
441 <para>Also see the
<varname>RootHash=
</varname> option in
442 <citerefentry><refentrytitle>systemd.exec
</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para>
444 <xi:include href=
"version-info.xml" xpointer=
"v233"/>
449 <term><option>--root-hash-sig=
</option></term>
451 <listitem><para>Takes a PKCS7 signature of the
<option>--root-hash=
</option> option.
452 The semantics are the same as for the
<varname>RootHashSignature=
</varname> option, see
453 <citerefentry><refentrytitle>systemd.exec
</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
456 <xi:include href=
"version-info.xml" xpointer=
"v246"/></listitem>
460 <term><option>--verity-data=
</option></term>
462 <listitem><para>Takes the path to a data integrity (dm-verity) file. This option enables data integrity checks
463 using dm-verity, if a root-hash is passed and if the used image itself does not contain the integrity data.
464 The integrity data must be matched by the root hash. If this option is not specified, but a file with the
465 <filename>.verity
</filename> suffix is found next to the image file, bearing otherwise the same name (except if
466 the image has the
<filename>.raw
</filename> suffix, in which case the verity data file must not have it in its name),
467 the verity data is read from it and automatically used.
</para>
469 <xi:include href=
"version-info.xml" xpointer=
"v246"/></listitem>
473 <term><option>--pivot-root=
</option></term>
475 <listitem><para>Pivot the specified directory to
<filename>/
</filename> inside the container, and either unmount the
476 container's old root, or pivot it to another specified directory. Takes one of: a path argument — in which case the
477 specified path will be pivoted to
<filename>/
</filename> and the old root will be unmounted; or a colon-separated pair
478 of new root path and pivot destination for the old root. The new root path will be pivoted to
<filename>/
</filename>,
479 and the old
<filename>/
</filename> will be pivoted to the other directory. Both paths must be absolute, and are resolved
480 in the container's file system namespace.
</para>
482 <para>This is for containers which have several bootable directories in them; for example, several
483 <ulink url=
"https://ostree.readthedocs.io/en/latest/">OSTree
</ulink> deployments. It emulates the
484 behavior of the boot loader and the initrd which normally select which directory to mount as the root
485 and start the container's PID
1 in.
</para>
487 <xi:include href=
"version-info.xml" xpointer=
"v233"/></listitem>
491 </refsect2><refsect2>
492 <title>Execution Options
</title>
496 <term><option>-a
</option></term>
497 <term><option>--as-pid2
</option></term>
499 <listitem><para>Invoke the shell or specified program as process ID (PID)
2 instead of PID
1 (init). By
500 default, if neither this option nor
<option>--boot
</option> is used, the selected program is run as the process
501 with PID
1, a mode only suitable for programs that are aware of the special semantics that the process with
502 PID
1 has on UNIX. For example, it needs to reap all processes reparented to it, and should implement
503 <command>sysvinit
</command> compatible signal handling (specifically: it needs to reboot on SIGINT, reexecute
504 on SIGTERM, reload configuration on SIGHUP, and so on). With
<option>--as-pid2
</option> a minimal stub init
505 process is run as PID
1 and the selected program is executed as PID
2 (and hence does not need to implement any
506 special semantics). The stub init process will reap processes as necessary and react appropriately to
507 signals. It is recommended to use this mode to invoke arbitrary commands in containers, unless they have been
508 modified to run correctly as PID
1. Or in other words: this switch should be used for pretty much all commands,
509 except when the command refers to an init or shell implementation, as these are generally capable of running
510 correctly as PID
1. This option may not be combined with
<option>--boot
</option>.
</para>
512 <xi:include href=
"version-info.xml" xpointer=
"v229"/>
517 <term><option>-b
</option></term>
518 <term><option>--boot
</option></term>
520 <listitem><para>Automatically search for an init program and invoke it as PID
1, instead of a shell or a user
521 supplied program. If this option is used, arguments specified on the command line are used as arguments for the
522 init program. This option may not be combined with
<option>--as-pid2
</option>.
</para>
524 <para>The following table explains the different modes of invocation and relationship to
525 <option>--as-pid2
</option> (see above):
</para>
528 <title>Invocation Mode
</title>
529 <tgroup cols='
2' align='left' colsep='
1' rowsep='
1'
>
530 <colspec colname=
"switch" />
531 <colspec colname=
"explanation" />
534 <entry>Switch
</entry>
535 <entry>Explanation
</entry>
540 <entry>Neither
<option>--as-pid2
</option> nor
<option>--boot
</option> specified
</entry>
541 <entry>The passed parameters are interpreted as the command line, which is executed as PID
1 in the container.
</entry>
545 <entry><option>--as-pid2
</option> specified
</entry>
546 <entry>The passed parameters are interpreted as the command line, which is executed as PID
2 in the container. A stub init process is run as PID
1.
</entry>
550 <entry><option>--boot
</option> specified
</entry>
551 <entry>An init program is automatically searched for and run as PID
1 in the container. The passed parameters are used as invocation parameters for this process.
</entry>
558 <para>Note that
<option>--boot
</option> is the default mode of operation if the
559 <filename>systemd-nspawn@.service
</filename> template unit file is used.
</para>
564 <term><option>--chdir=
</option></term>
566 <listitem><para>Change to the specified working directory before invoking the process in the container. Expects
567 an absolute path in the container's file system namespace.
</para>
569 <xi:include href=
"version-info.xml" xpointer=
"v229"/></listitem>
573 <term><option>-E
<replaceable>NAME
</replaceable>[=
<replaceable>VALUE
</replaceable>]
</option></term>
574 <term><option>--setenv=
<replaceable>NAME
</replaceable>[=
<replaceable>VALUE
</replaceable>]
</option></term>
576 <listitem><para>Specifies an environment variable to pass to the init process in the container. This
577 may be used to override the default variables or to set additional variables. It may be used more
578 than once to set multiple variables. When
<literal>=
</literal> and
<replaceable>VALUE
</replaceable>
579 are omitted, the value of the variable with the same name in the program environment will be used.
582 <xi:include href=
"version-info.xml" xpointer=
"v209"/></listitem>
586 <term><option>-u
</option></term>
587 <term><option>--user=
</option></term>
589 <listitem><para>After transitioning into the container, change to the specified user defined in the
590 container's user database. Like all other systemd-nspawn features, this is not a security feature and
591 provides protection against accidental destructive operations only.
</para></listitem>
595 <term><option>--kill-signal=
</option></term>
597 <listitem><para>Specify the process signal to send to the container's PID
1 when nspawn itself receives
598 <constant>SIGTERM
</constant>, in order to trigger an orderly shutdown of the container. Defaults to
599 <constant>SIGRTMIN+
3</constant> if
<option>--boot
</option> is used (on systemd-compatible init systems
600 <constant>SIGRTMIN+
3</constant> triggers an orderly shutdown). If
<option>--boot
</option> is not used and this
601 option is not specified the container's processes are terminated abruptly via
<constant>SIGKILL
</constant>. For
602 a list of valid signals, see
<citerefentry
603 project='man-pages'
><refentrytitle>signal
</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
</para>
605 <xi:include href=
"version-info.xml" xpointer=
"v220"/></listitem>
609 <term><option>--notify-ready=
</option></term>
611 <listitem><para>Configures support for notifications from the container's init process.
612 <option>--notify-ready=
</option> takes a boolean (
<option>no
</option> and
<option>yes
</option>).
613 With option
<option>no
</option> systemd-nspawn notifies systemd
614 with a
<literal>READY=
1</literal> message when the init process is created.
615 With option
<option>yes
</option> systemd-nspawn waits for the
616 <literal>READY=
1</literal> message from the init process in the container
617 before sending its own to systemd. For more details about notifications
618 see
<citerefentry><refentrytitle>sd_notify
</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para>
620 <xi:include href=
"version-info.xml" xpointer=
"v231"/></listitem>
624 <term><option>--suppress-sync=
</option></term>
626 <listitem><para>Expects a boolean argument. If true, turns off any form of on-disk file system
627 synchronization for the container payload. This means all system calls such as
<citerefentry
628 project='man-pages'
><refentrytitle>sync
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
629 <function>fsync()
</function>,
<function>syncfs()
</function>, … will execute no operation, and the
630 <constant>O_SYNC
</constant>/
<constant>O_DSYNC
</constant> flags to
<citerefentry
631 project='man-pages'
><refentrytitle>open
</refentrytitle><manvolnum>2</manvolnum></citerefentry> and
632 related calls will be made unavailable. This is potentially dangerous, as assumed data integrity
633 guarantees to the container payload are not actually enforced (i.e. data assumed to have been written
634 to disk might be lost if the system is shut down abnormally). However, this can dramatically improve
635 container runtime performance – as long as these guarantees are not required or desirable, for
636 example because any data written by the container is of temporary, redundant nature, or just an
637 intermediary artifact that will be further processed and finalized by a later step in a
638 pipeline. Defaults to false.
</para>
640 <xi:include href=
"version-info.xml" xpointer=
"v250"/></listitem>
644 </refsect2><refsect2>
645 <title>System Identity Options
</title>
649 <term><option>-M
</option></term>
650 <term><option>--machine=
</option></term>
652 <listitem><para>Sets the machine name for this container. This
653 name may be used to identify this container during its runtime
654 (for example in tools like
655 <citerefentry><refentrytitle>machinectl
</refentrytitle><manvolnum>1</manvolnum></citerefentry>
656 and similar), and is used to initialize the container's
657 hostname (which the container can choose to override,
658 however). If not specified, the last component of the root
659 directory path of the container is used, possibly suffixed
660 with a random identifier in case
<option>--ephemeral
</option>
661 mode is selected. If the root directory selected is the host's
662 root directory the host's hostname is used as default
665 <xi:include href=
"version-info.xml" xpointer=
"v202"/></listitem>
669 <term><option>--hostname=
</option></term>
671 <listitem><para>Controls the hostname to set within the container, if different from the machine name. Expects
672 a valid hostname as argument. If this option is used, the kernel hostname of the container will be set to this
673 value, otherwise it will be initialized to the machine name as controlled by the
<option>--machine=
</option>
674 option described above. The machine name is used for various aspect of identification of the container from the
675 outside, the kernel hostname configurable with this option is useful for the container to identify itself from
676 the inside. It is usually a good idea to keep both forms of identification synchronized, in order to avoid
677 confusion. It is hence recommended to avoid usage of this option, and use
<option>--machine=
</option>
678 exclusively. Note that regardless whether the container's hostname is initialized from the name set with
679 <option>--hostname=
</option> or the one set with
<option>--machine=
</option>, the container can later override
680 its kernel hostname freely on its own as well.
</para>
682 <xi:include href=
"version-info.xml" xpointer=
"v239"/>
687 <term><option>--uuid=
</option></term>
689 <listitem><para>Set the specified UUID for the container. The
690 init system will initialize
691 <filename>/etc/machine-id
</filename> from this if this file is
692 not set yet. Note that this option takes effect only if
693 <filename>/etc/machine-id
</filename> in the container is
694 unpopulated.
</para></listitem>
698 </refsect2><refsect2>
699 <title>Property Options
</title>
703 <term><option>-S
</option></term>
704 <term><option>--slice=
</option></term>
706 <listitem><para>Make the container part of the specified slice, instead of the default
707 <filename>machine.slice
</filename>. This applies only if the machine is run in its own scope unit, i.e. if
708 <option>--keep-unit
</option> isn't used.
</para>
710 <xi:include href=
"version-info.xml" xpointer=
"v206"/>
715 <term><option>--property=
</option></term>
717 <listitem><para>Set a unit property on the scope unit to register for the machine. This applies only if the
718 machine is run in its own scope unit, i.e. if
<option>--keep-unit
</option> isn't used. Takes unit property
719 assignments in the same format as
<command>systemctl set-property
</command>. This is useful to set memory
720 limits and similar for the container.
</para>
722 <xi:include href=
"version-info.xml" xpointer=
"v220"/>
727 <term><option>--register=
</option></term>
729 <listitem><para>Controls whether the container is registered with
730 <citerefentry><refentrytitle>systemd-machined
</refentrytitle><manvolnum>8</manvolnum></citerefentry>. Takes a
731 boolean argument, which defaults to
<literal>yes
</literal>. This option should be enabled when the container
732 runs a full Operating System (more specifically: a system and service manager as PID
1), and is useful to
733 ensure that the container is accessible via
734 <citerefentry><refentrytitle>machinectl
</refentrytitle><manvolnum>1</manvolnum></citerefentry> and shown by
735 tools such as
<citerefentry
736 project='man-pages'
><refentrytitle>ps
</refentrytitle><manvolnum>1</manvolnum></citerefentry>. If the container
737 does not run a service manager, it is recommended to set this option to
738 <literal>no
</literal>.
</para>
740 <xi:include href=
"version-info.xml" xpointer=
"v209"/></listitem>
744 <term><option>--keep-unit
</option></term>
746 <listitem><para>Instead of creating a transient scope unit to run the container in, simply use the service or
747 scope unit
<command>systemd-nspawn
</command> has been invoked in. If
<option>--register=yes
</option> is set
748 this unit is registered with
749 <citerefentry><refentrytitle>systemd-machined
</refentrytitle><manvolnum>8</manvolnum></citerefentry>. This
750 switch should be used if
<command>systemd-nspawn
</command> is invoked from within a service unit, and the
751 service unit's sole purpose is to run a single
<command>systemd-nspawn
</command> container. This option is not
752 available if run from a user session.
</para>
753 <para>Note that passing
<option>--keep-unit
</option> disables the effect of
<option>--slice=
</option> and
754 <option>--property=
</option>. Use
<option>--keep-unit
</option> and
<option>--register=no
</option> in
755 combination to disable any kind of unit allocation or registration with
756 <command>systemd-machined
</command>.
</para>
758 <xi:include href=
"version-info.xml" xpointer=
"v209"/></listitem>
762 </refsect2><refsect2>
763 <title>User Namespacing Options
</title>
767 <term><option>--private-users=
</option></term>
769 <listitem><para>Controls user namespacing. If enabled, the container will run with its own private set of UNIX
770 user and group ids (UIDs and GIDs). This involves mapping the private UIDs/GIDs used in the container (starting
771 with the container's root user
0 and up) to a range of UIDs/GIDs on the host that are not used for other
772 purposes (usually in the range beyond the host's UID/GID
65536). The parameter may be specified as follows:
</para>
775 <listitem><para>If one or two colon-separated numbers are specified, user namespacing is turned on. The first
776 parameter specifies the first host UID/GID to assign to the container, the second parameter specifies the
777 number of host UIDs/GIDs to assign to the container. If the second parameter is omitted,
65536 UIDs/GIDs are
778 assigned.
</para></listitem>
780 <listitem><para>If the parameter is
<literal>yes
</literal>, user namespacing is turned on. The
781 UID/GID range to use is determined automatically from the file ownership of the root directory of
782 the container's directory tree. To use this option, make sure to prepare the directory tree in
783 advance, and ensure that all files and directories in it are owned by UIDs/GIDs in the range you'd
784 like to use. Also, make sure that used file ACLs exclusively reference UIDs/GIDs in the appropriate
785 range. In this mode, the number of UIDs/GIDs assigned to the container is
65536, and the owner
786 UID/GID of the root directory must be a multiple of
65536.
</para></listitem>
788 <listitem><para>If the parameter is
<literal>no
</literal>, user namespacing is turned off. This is
792 <listitem><para>If the parameter is
<literal>identity
</literal>, user namespacing is employed with
793 an identity mapping for the first
65536 UIDs/GIDs. This is mostly equivalent to
794 <option>--private-users=
0:
65536</option>. While it does not provide UID/GID isolation, since all
795 host and container UIDs/GIDs are chosen identically it does provide process capability isolation,
796 and hence is often a good choice if proper user namespacing with distinct UID maps is not
797 appropriate.
</para></listitem>
799 <listitem><para>The special value
<literal>pick
</literal> turns on user namespacing. In this case
800 the UID/GID range is automatically chosen. As first step, the file owner UID/GID of the root
801 directory of the container's directory tree is read, and it is checked that no other container is
802 currently using it. If this check is successful, the UID/GID range determined this way is used,
803 similarly to the behavior if
<literal>yes
</literal> is specified. If the check is not successful
804 (and thus the UID/GID range indicated in the root directory's file owner is already used elsewhere)
805 a new – currently unused – UID/GID range of
65536 UIDs/GIDs is randomly chosen between the host
806 UID/GIDs of
524288 and
1878982656, always starting at a multiple of
65536, and, if possible,
807 consistently hashed from the machine name. This setting implies
808 <option>--private-users-ownership=auto
</option> (see below), which possibly has the effect that the
809 files and directories in the container's directory tree will be owned by the appropriate users of
810 the range picked. Using this option makes user namespace behavior fully automatic. Note that the
811 first invocation of a previously unused container image might result in picking a new UID/GID range
812 for it, and thus in the (possibly expensive) file ownership adjustment operation. However,
813 subsequent invocations of the container will be cheap (unless of course the picked UID/GID range is
814 assigned to a different use by then).
</para></listitem>
817 <para>It is recommended to assign at least
65536 UIDs/GIDs to each container, so that the usable UID/GID range in the
818 container covers
16 bit. For best security, do not assign overlapping UID/GID ranges to multiple containers. It is
819 hence a good idea to use the upper
16 bit of the host
32-bit UIDs/GIDs as container identifier, while the lower
16
820 bit encode the container UID/GID used. This is in fact the behavior enforced by the
821 <option>--private-users=pick
</option> option.
</para>
823 <para>When user namespaces are used, the GID range assigned to each container is always chosen identical to the
826 <para>In most cases, using
<option>--private-users=pick
</option> is the recommended option as it enhances
827 container security massively and operates fully automatically in most cases.
</para>
829 <para>Note that the picked UID/GID range is not written to
<filename>/etc/passwd
</filename> or
830 <filename>/etc/group
</filename>. In fact, the allocation of the range is not stored persistently anywhere,
831 except in the file ownership of the files and directories of the container.
</para>
833 <para>Note that when user namespacing is used file ownership on disk reflects this, and all of the container's
834 files and directories are owned by the container's effective user and group IDs. This means that copying files
835 from and to the container image requires correction of the numeric UID/GID values, according to the UID/GID
836 shift applied.
</para>
838 <xi:include href=
"version-info.xml" xpointer=
"v220"/></listitem>
842 <term><option>--private-users-ownership=
</option></term>
844 <listitem><para>Controls how to adjust the container image's UIDs and GIDs to match the UID/GID range
845 chosen with
<option>--private-users=
</option>, see above. Takes one of
<literal>off
</literal> (to
846 leave the image as is),
<literal>chown
</literal> (to recursively
<function>chown()
</function> the
847 container's directory tree as needed),
<literal>map
</literal> (in order to use transparent ID mapping
848 mounts) or
<literal>auto
</literal> for automatically using
<literal>map
</literal> where available and
849 <literal>chown
</literal> where not.
</para>
851 <para>If
<literal>chown
</literal> is selected, all files and directories in the container's directory
852 tree will be adjusted so that they are owned by the appropriate UIDs/GIDs selected for the container
853 (see above). This operation is potentially expensive, as it involves iterating through the full
854 directory tree of the container. Besides actual file ownership, file ACLs are adjusted as
857 <para>Typically
<literal>map
</literal> is the best choice, since it transparently maps UIDs/GIDs in
858 memory as needed without modifying the image, and without requiring an expensive recursive adjustment
859 operation. However, it is not available for all file systems, currently.
</para>
861 <para>The
<option>--private-users-ownership=auto
</option> option is implied if
862 <option>--private-users=pick
</option> is used. This option has no effect if user namespacing is not
865 <xi:include href=
"version-info.xml" xpointer=
"v230"/></listitem>
869 <term><option>-U
</option></term>
871 <listitem><para>If the kernel supports the user namespaces feature, equivalent to
872 <option>--private-users=pick --private-users-ownership=auto
</option>, otherwise equivalent to
873 <option>--private-users=no
</option>.
</para>
875 <para>Note that
<option>-U
</option> is the default if the
876 <filename>systemd-nspawn@.service
</filename> template unit file is used.
</para>
878 <para>Note: it is possible to undo the effect of
<option>--private-users-ownership=chown
</option> (or
879 <option>-U
</option>) on the file system by redoing the operation with the first UID of
0:
</para>
881 <programlisting>systemd-nspawn … --private-users=
0 --private-users-ownership=chown
</programlisting>
883 <xi:include href=
"version-info.xml" xpointer=
"v230"/>
889 </refsect2><refsect2>
890 <title>Networking Options
</title>
895 <term><option>--private-network
</option></term>
897 <listitem><para>Disconnect networking of the container from
898 the host. This makes all network interfaces unavailable in the
899 container, with the exception of the loopback device and those
900 specified with
<option>--network-interface=
</option> and
901 configured with
<option>--network-veth
</option>. If this
902 option is specified, the
<constant>CAP_NET_ADMIN
</constant> capability will be
903 added to the set of capabilities the container retains. The
904 latter may be disabled by using
<option>--drop-capability=
</option>.
905 If this option is not specified (or implied by one of the options
906 listed below), the container will have full access to the host network.
911 <term><option>--network-interface=
</option></term>
913 <listitem><para>Assign the specified network interface to the container. Either takes a single
914 interface name, referencing the name on the host, or a colon-separated pair of interfaces, in which
915 case the first one references the name on the host, and the second one the name in the container.
916 When the container terminates, the interface is moved back to the calling namespace and renamed to
917 its original name. Note that
<option>--network-interface=
</option> implies
918 <option>--private-network
</option>. This option may be used more than once to add multiple network
919 interfaces to the container.
</para>
921 <para>Note that any network interface specified this way must already exist at the time the container
922 is started. If the container shall be started automatically at boot via a
923 <filename>systemd-nspawn@.service
</filename> unit file instance, it might hence make sense to add a
924 unit file drop-in to the service instance
925 (e.g.
<filename>/etc/systemd/system/systemd-nspawn@foobar.service.d/
50-network.conf
</filename>) with
926 contents like the following:
</para>
928 <programlisting>[Unit]
929 Wants=sys-subsystem-net-devices-ens1.device
930 After=sys-subsystem-net-devices-ens1.device
</programlisting>
932 <para>This will make sure that activation of the container service will be delayed until the
933 <literal>ens1
</literal> network interface has shown up. This is required since hardware probing is
934 fully asynchronous, and network interfaces might be discovered only later during the boot process,
935 after the container would normally be started without these explicit dependencies.
</para>
937 <xi:include href=
"version-info.xml" xpointer=
"v209"/>
942 <term><option>--network-macvlan=
</option></term>
944 <listitem><para>Create a
<literal>macvlan
</literal> interface of the specified Ethernet network
945 interface and add it to the container. Either takes a single interface name, referencing the name
946 on the host, or a colon-separated pair of interfaces, in which case the first one references the name
947 on the host, and the second one the name in the container. A
<literal>macvlan
</literal> interface is
948 a virtual interface that adds a second MAC address to an existing physical Ethernet link. If the
949 container interface name is not defined, the interface in the container will be named after the
950 interface on the host, prefixed with
<literal>mv-
</literal>. Note that
951 <option>--network-macvlan=
</option> implies
<option>--private-network
</option>. This option may be
952 used more than once to add multiple network interfaces to the container.
</para>
954 <para>As with
<option>--network-interface=
</option>, the underlying Ethernet network interface must
955 already exist at the time the container is started, and thus similar unit file drop-ins as described
956 above might be useful.
</para>
958 <xi:include href=
"version-info.xml" xpointer=
"v211"/></listitem>
962 <term><option>--network-ipvlan=
</option></term>
964 <listitem><para>Create an
<literal>ipvlan
</literal> interface of the specified Ethernet network
965 interface and add it to the container. Either takes a single interface name, referencing the name on
966 the host, or a colon-separated pair of interfaces, in which case the first one references the name
967 on the host, and the second one the name in the container. An
<literal>ipvlan
</literal> interface is
969 similar to a
<literal>macvlan
</literal> interface, which uses the same MAC address as the underlying
970 interface. If the container interface name is not defined, the interface in the container will be
971 named after the interface on the host, prefixed
972 with
<literal>iv-
</literal>. Note that
<option>--network-ipvlan=
</option> implies
973 <option>--private-network
</option>. This option may be used more than once to add multiple network
974 interfaces to the container.
</para>
976 <para>As with
<option>--network-interface=
</option>, the underlying Ethernet network interface must
977 already exist at the time the container is started, and thus similar unit file drop-ins as described
978 above might be useful.
</para>
980 <xi:include href=
"version-info.xml" xpointer=
"v219"/></listitem>
984 <term><option>-n
</option></term>
985 <term><option>--network-veth
</option></term>
987 <listitem><para>Create a virtual Ethernet link (
<literal>veth
</literal>) between host and container. The host
988 side of the Ethernet link will be available as a network interface named after the container's name (as
989 specified with
<option>--machine=
</option>), prefixed with
<literal>ve-
</literal>. The container side of the
990 Ethernet link will be named
<literal>host0
</literal>. The
<option>--network-veth
</option> option implies
991 <option>--private-network
</option>.
</para>
994 <citerefentry><refentrytitle>systemd-networkd.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
995 includes by default a network file
<filename>/usr/lib/systemd/network/
80-container-ve.network
</filename>
996 matching the host-side interfaces created this way, which contains settings to enable automatic address
997 provisioning on the created virtual link via DHCP, as well as automatic IP routing onto the host's external
998 network interfaces. It also contains
<filename>/usr/lib/systemd/network/
80-container-host0.network
</filename>
999 matching the container-side interface created this way, containing settings to enable client side address
1000 assignment via DHCP. In case
<filename>systemd-networkd
</filename> is running on both the host and inside the
1001 container, automatic IP communication from the container to the host is thus available, with further
1002 connectivity to the external network.
</para>
1004 <para>Note that
<option>--network-veth
</option> is the default if the
1005 <filename>systemd-nspawn@.service
</filename> template unit file is used.
</para>
1007 <para>Note that on Linux network interface names may have a length of
15 characters at maximum, while
1008 container names may have a length up to
64 characters. As this option derives the host-side interface
1009 name from the container name the name is possibly truncated. Thus, care needs to be taken to ensure
1010 that interface names remain unique in this case, or even better container names are generally not
1011 chosen longer than
12 characters, to avoid the truncation. If the name is truncated,
1012 <command>systemd-nspawn
</command> will automatically append a
4-digit hash value to the name to
1013 reduce the chance of collisions. However, the hash algorithm is not collision-free. (See
1014 <citerefentry><refentrytitle>systemd.net-naming-scheme
</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1015 for details on older naming algorithms for this interface). Alternatively, the
1016 <option>--network-veth-extra=
</option> option may be used, which allows free configuration of the
1017 host-side interface name independently of the container name — but might require a bit more
1018 additional configuration in case bridging in a fashion similar to
<option>--network-bridge=
</option>
1021 <xi:include href=
"version-info.xml" xpointer=
"v209"/>
1026 <term><option>--network-veth-extra=
</option></term>
1028 <listitem><para>Adds an additional virtual Ethernet link
1029 between host and container. Takes a colon-separated pair of
1030 host interface name and container interface name. The latter
1031 may be omitted in which case the container and host sides will
1032 be assigned the same name. This switch is independent of
1033 <option>--network-veth
</option>, and — in contrast — may be
1034 used multiple times, and allows configuration of the network
1035 interface names. Note that
<option>--network-bridge=
</option>
1036 has no effect on interfaces created with
1037 <option>--network-veth-extra=
</option>.
</para>
1039 <xi:include href=
"version-info.xml" xpointer=
"v228"/></listitem>
1043 <term><option>--network-bridge=
</option></term>
1045 <listitem><para>Adds the host side of the Ethernet link created with
<option>--network-veth
</option>
1046 to the specified Ethernet bridge interface. Expects a valid network interface name of a bridge device
1047 as argument. Note that
<option>--network-bridge=
</option> implies
<option>--network-veth
</option>. If
1048 this option is used, the host side of the Ethernet link will use the
<literal>vb-
</literal> prefix
1049 instead of
<literal>ve-
</literal>. Regardless of the used naming prefix the same network interface
1050 name length limits imposed by Linux apply, along with the complications this creates (for details see
1053 <para>As with
<option>--network-interface=
</option>, the underlying bridge network interface must
1054 already exist at the time the container is started, and thus similar unit file drop-ins as described
1055 above might be useful.
</para>
1057 <xi:include href=
"version-info.xml" xpointer=
"v209"/></listitem>
1061 <term><option>--network-zone=
</option></term>
1063 <listitem><para>Creates a virtual Ethernet link (
<literal>veth
</literal>) to the container and adds it to an
1064 automatically managed Ethernet bridge interface. The bridge interface is named after the passed argument,
1065 prefixed with
<literal>vz-
</literal>. The bridge interface is automatically created when the first container
1066 configured for its name is started, and is automatically removed when the last container configured for its
1067 name exits. Hence, each bridge interface configured this way exists only as long as there's at least one
1068 container referencing it running. This option is very similar to
<option>--network-bridge=
</option>, besides
1069 this automatic creation/removal of the bridge device.
</para>
1071 <para>This setting makes it easy to place multiple related containers on a common, virtual Ethernet-based
1072 broadcast domain, here called a
"zone". Each container may only be part of one zone, but each zone may contain
1073 any number of containers. Each zone is referenced by its name. Names may be chosen freely (as long as they form
1074 valid network interface names when prefixed with
<literal>vz-
</literal>), and it is sufficient to pass the same
1075 name to the
<option>--network-zone=
</option> switch of the various concurrently running containers to join
1076 them in one zone.
</para>
1079 <citerefentry><refentrytitle>systemd-networkd.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1080 includes by default a network file
<filename>/usr/lib/systemd/network/
80-container-vz.network
</filename>
1081 matching the bridge interfaces created this way, which contains settings to enable automatic address
1082 provisioning on the created virtual network via DHCP, as well as automatic IP routing onto the host's external
1083 network interfaces. Using
<option>--network-zone=
</option> is hence in most cases fully automatic and
1084 sufficient to connect multiple local containers in a joined broadcast domain to the host, with further
1085 connectivity to the external network.
</para>
1087 <xi:include href=
"version-info.xml" xpointer=
"v230"/>
1092 <term><option>--network-namespace-path=
</option></term>
1094 <listitem><para>Takes the path to a file representing a kernel
1095 network namespace that the container shall run in. The specified path
1096 should refer to a (possibly bind-mounted) network namespace file, as
1097 exposed by the kernel below
<filename>/proc/$PID/ns/net
</filename>.
1098 This makes the container enter the given network namespace. One of the
1099 typical use cases is to give a network namespace under
1100 <filename>/run/netns
</filename> created by
<citerefentry
1101 project='man-pages'
><refentrytitle>ip-netns
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1102 for example,
<option>--network-namespace-path=/run/netns/foo
</option>.
1103 Note that this option cannot be used together with other
1104 network-related options, such as
<option>--private-network
</option>
1105 or
<option>--network-interface=
</option>.
</para>
1107 <xi:include href=
"version-info.xml" xpointer=
"v236"/></listitem>
1111 <term><option>-p
</option></term>
1112 <term><option>--port=
</option></term>
1114 <listitem><para>If private networking is enabled, maps an IP
1115 port on the host onto an IP port on the container. Takes a
1116 protocol specifier (either
<literal>tcp
</literal> or
1117 <literal>udp
</literal>), separated by a colon from a host port
1118 number in the range
1 to
65535, separated by a colon from a
1119 container port number in the range from
1 to
65535. The
1120 protocol specifier and its separating colon may be omitted, in
1121 which case
<literal>tcp
</literal> is assumed. The container
1122 port number and its colon may be omitted, in which case the
1123 same port as the host port is implied. This option is only
1124 supported if private networking is used, such as with
1125 <option>--network-veth
</option>,
<option>--network-zone=
</option>
1126 <option>--network-bridge=
</option>.
</para>
1128 <xi:include href=
"version-info.xml" xpointer=
"v219"/></listitem>
1132 </refsect2><refsect2>
1133 <title>Security Options
</title>
1137 <term><option>--capability=
</option></term>
1139 <listitem><para>List one or more additional capabilities to grant the container. Takes a
1140 comma-separated list of capability names, see
<citerefentry
1141 project='man-pages'
><refentrytitle>capabilities
</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1142 for more information. Note that the following capabilities will be granted in any way:
1143 <constant>CAP_AUDIT_CONTROL
</constant>,
<constant>CAP_AUDIT_WRITE
</constant>,
1144 <constant>CAP_CHOWN
</constant>,
<constant>CAP_DAC_OVERRIDE
</constant>,
1145 <constant>CAP_DAC_READ_SEARCH
</constant>,
<constant>CAP_FOWNER
</constant>,
1146 <constant>CAP_FSETID
</constant>,
<constant>CAP_IPC_OWNER
</constant>,
<constant>CAP_KILL
</constant>,
1147 <constant>CAP_LEASE
</constant>,
<constant>CAP_LINUX_IMMUTABLE
</constant>,
1148 <constant>CAP_MKNOD
</constant>,
<constant>CAP_NET_BIND_SERVICE
</constant>,
1149 <constant>CAP_NET_BROADCAST
</constant>,
<constant>CAP_NET_RAW
</constant>,
1150 <constant>CAP_SETFCAP
</constant>,
<constant>CAP_SETGID
</constant>,
<constant>CAP_SETPCAP
</constant>,
1151 <constant>CAP_SETUID
</constant>,
<constant>CAP_SYS_ADMIN
</constant>,
1152 <constant>CAP_SYS_BOOT
</constant>,
<constant>CAP_SYS_CHROOT
</constant>,
1153 <constant>CAP_SYS_NICE
</constant>,
<constant>CAP_SYS_PTRACE
</constant>,
1154 <constant>CAP_SYS_RESOURCE
</constant>,
<constant>CAP_SYS_TTY_CONFIG
</constant>. Also
1155 <constant>CAP_NET_ADMIN
</constant> is retained if
<option>--private-network
</option> is specified.
1156 If the special value
<literal>all
</literal> is passed, all capabilities are retained.
</para>
1158 <para>If the special value of
<literal>help
</literal> is passed, the program will print known
1159 capability names and exit.
</para>
1161 <para>This option sets the bounding set of capabilities which
1162 also limits the ambient capabilities as given with the
1163 <option>--ambient-capability=
</option>.
</para>
1165 <xi:include href=
"version-info.xml" xpointer=
"v186"/></listitem>
1169 <term><option>--drop-capability=
</option></term>
1171 <listitem><para>Specify one or more additional capabilities to
1172 drop for the container. This allows running the container with
1173 fewer capabilities than the default (see
1176 <para>If the special value of
<literal>help
</literal> is passed, the program will print known
1177 capability names and exit.
</para>
1179 <para>This option sets the bounding set of capabilities which
1180 also limits the ambient capabilities as given with the
1181 <option>--ambient-capability=
</option>.
</para>
1183 <xi:include href=
"version-info.xml" xpointer=
"v209"/></listitem>
1187 <term><option>--ambient-capability=
</option></term>
1189 <listitem><para>Specify one or more additional capabilities to
1190 pass in the inheritable and ambient set to the program started
1191 within the container. The value
<literal>all
</literal> is not
1192 supported for this setting.
</para>
1194 <para>All capabilities specified here must be in the set
1195 allowed with the
<option>--capability=
</option> and
1196 <option>--drop-capability=
</option> options. Otherwise, an
1197 error message will be shown.
</para>
1199 <para>This option cannot be combined with the boot mode of the
1200 container (as requested via
<option>--boot
</option>).
</para>
1202 <para>If the special value of
<literal>help
</literal> is
1203 passed, the program will print known capability names and
1206 <xi:include href=
"version-info.xml" xpointer=
"v248"/></listitem>
1210 <term><option>--no-new-privileges=
</option></term>
1212 <listitem><para>Takes a boolean argument. Specifies the value of the
1213 <constant>PR_SET_NO_NEW_PRIVS
</constant> flag for the container payload. Defaults to off. When turned
1214 on the payload code of the container cannot acquire new privileges, i.e. the
"setuid" file bit as
1215 well as file system capabilities will not have an effect anymore. See
<citerefentry
1216 project='man-pages'
><refentrytitle>prctl
</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
1217 details about this flag.
</para>
1219 <xi:include href=
"version-info.xml" xpointer=
"v239"/></listitem>
1223 <term><option>--system-call-filter=
</option></term> <listitem><para>Alter the system call filter
1224 applied to containers. Takes a space-separated list of system call names or group names (the latter
1225 prefixed with
<literal>@
</literal>, as listed by the
<command>syscall-filter
</command> command of
1226 <citerefentry><refentrytitle>systemd-analyze
</refentrytitle><manvolnum>1</manvolnum></citerefentry>). Passed
1227 system calls will be permitted. The list may optionally be prefixed by
<literal>~
</literal>, in which
1228 case all listed system calls are prohibited. If this command line option is used multiple times the
1229 configured lists are combined. If both a positive and a negative list (that is one system call list
1230 without and one with the
<literal>~
</literal> prefix) are configured, the negative list takes
1231 precedence over the positive list. Note that
<command>systemd-nspawn
</command> always implements a
1232 system call allow list (as opposed to a deny list!), and this command line option hence adds or
1233 removes entries from the default allow list, depending on the
<literal>~
</literal> prefix. Note that
1234 the applied system call filter is also altered implicitly if additional capabilities are passed using
1235 the
<command>--capabilities=
</command>.
</para>
1237 <xi:include href=
"version-info.xml" xpointer=
"v235"/></listitem>
1241 <term><option>-Z
</option></term>
1242 <term><option>--selinux-context=
</option></term>
1244 <listitem><para>Sets the SELinux security context to be used
1245 to label processes in the container.
</para>
1247 <xi:include href=
"version-info.xml" xpointer=
"v209"/>
1252 <term><option>-L
</option></term>
1253 <term><option>--selinux-apifs-context=
</option></term>
1255 <listitem><para>Sets the SELinux security context to be used
1256 to label files in the virtual API file systems in the
1259 <xi:include href=
"version-info.xml" xpointer=
"v209"/>
1264 </refsect2><refsect2>
1265 <title>Resource Options
</title>
1270 <term><option>--rlimit=
</option></term>
1272 <listitem><para>Sets the specified POSIX resource limit for the container payload. Expects an assignment of the
1274 <literal><replaceable>LIMIT
</replaceable>=
<replaceable>SOFT
</replaceable>:
<replaceable>HARD
</replaceable></literal>
1275 or
<literal><replaceable>LIMIT
</replaceable>=
<replaceable>VALUE
</replaceable></literal>, where
1276 <replaceable>LIMIT
</replaceable> should refer to a resource limit type, such as
1277 <constant>RLIMIT_NOFILE
</constant> or
<constant>RLIMIT_NICE
</constant>. The
<replaceable>SOFT
</replaceable> and
1278 <replaceable>HARD
</replaceable> fields should refer to the numeric soft and hard resource limit values. If the
1279 second form is used,
<replaceable>VALUE
</replaceable> may specify a value that is used both as soft and hard
1280 limit. In place of a numeric value the special string
<literal>infinity
</literal> may be used to turn off
1281 resource limiting for the specific type of resource. This command line option may be used multiple times to
1282 control limits on multiple limit types. If used multiple times for the same limit type, the last use
1283 wins. For details about resource limits see
<citerefentry
1284 project='man-pages'
><refentrytitle>setrlimit
</refentrytitle><manvolnum>2</manvolnum></citerefentry>. By default
1285 resource limits for the container's init process (PID
1) are set to the same values the Linux kernel originally
1286 passed to the host init system. Note that some resource limits are enforced on resources counted per user, in
1287 particular
<constant>RLIMIT_NPROC
</constant>. This means that unless user namespacing is deployed
1288 (i.e.
<option>--private-users=
</option> is used, see above), any limits set will be applied to the resource
1289 usage of the same user on all local containers as well as the host. This means particular care needs to be
1290 taken with these limits as they might be triggered by possibly less trusted code. Example:
1291 <literal>--rlimit=RLIMIT_NOFILE=
8192:
16384</literal>.
</para>
1293 <xi:include href=
"version-info.xml" xpointer=
"v239"/></listitem>
1297 <term><option>--oom-score-adjust=
</option></term>
1299 <listitem><para>Changes the OOM (
"Out Of Memory") score adjustment value for the container payload. This controls
1300 <filename>/proc/self/oom_score_adj
</filename> which influences the preference with which this container is
1301 terminated when memory becomes scarce. For details see
<citerefentry
1302 project='man-pages'
><refentrytitle>proc
</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Takes an
1303 integer in the range -
1000…
1000.
</para>
1305 <xi:include href=
"version-info.xml" xpointer=
"v239"/></listitem>
1309 <term><option>--cpu-affinity=
</option></term>
1311 <listitem><para>Controls the CPU affinity of the container payload. Takes a comma separated list of CPU numbers
1312 or number ranges (the latter's start and end value separated by dashes). See
<citerefentry
1313 project='man-pages'
><refentrytitle>sched_setaffinity
</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
1316 <xi:include href=
"version-info.xml" xpointer=
"v239"/></listitem>
1320 <term><option>--personality=
</option></term>
1322 <listitem><para>Control the architecture (
"personality")
1324 <citerefentry project='man-pages'
><refentrytitle>uname
</refentrytitle><manvolnum>2</manvolnum></citerefentry>
1325 in the container. Currently, only
<literal>x86
</literal> and
1326 <literal>x86-
64</literal> are supported. This is useful when
1327 running a
32-bit container on a
64-bit host. If this setting
1328 is not used, the personality reported in the container is the
1329 same as the one reported on the host.
</para>
1331 <xi:include href=
"version-info.xml" xpointer=
"v209"/></listitem>
1335 </refsect2><refsect2>
1336 <title>Integration Options
</title>
1340 <term><option>--resolv-conf=
</option></term>
1342 <listitem><para>Configures how
<filename>/etc/resolv.conf
</filename> inside of the container shall be
1343 handled (i.e. DNS configuration synchronization from host to container). Takes one of
1344 <literal>off
</literal>,
<literal>copy-host
</literal>,
<literal>copy-static
</literal>,
1345 <literal>copy-uplink
</literal>,
<literal>copy-stub
</literal>,
<literal>replace-host
</literal>,
1346 <literal>replace-static
</literal>,
<literal>replace-uplink
</literal>,
1347 <literal>replace-stub
</literal>,
<literal>bind-host
</literal>,
<literal>bind-static
</literal>,
1348 <literal>bind-uplink
</literal>,
<literal>bind-stub
</literal>,
<literal>delete
</literal> or
1349 <literal>auto
</literal>.
</para>
1351 <para>If set to
<literal>off
</literal> the
<filename>/etc/resolv.conf
</filename> file in the
1352 container is left as it is included in the image, and neither modified nor bind mounted over.
</para>
1354 <para>If set to
<literal>copy-host
</literal>, the
<filename>/etc/resolv.conf
</filename> file from the
1355 host is copied into the container, unless the file exists already and is not a regular file (e.g. a
1356 symlink). Similarly, if
<literal>replace-host
</literal> is used the file is copied, replacing any
1357 existing inode, including symlinks. Similarly, if
<literal>bind-host
</literal> is used, the file is
1358 bind mounted from the host into the container.
</para>
1360 <para>If set to
<literal>copy-static
</literal>,
<literal>replace-static
</literal> or
1361 <literal>bind-static
</literal> the static
<filename>resolv.conf
</filename> file supplied with
1362 <citerefentry><refentrytitle>systemd-resolved.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1363 (specifically:
<filename>/usr/lib/systemd/resolv.conf
</filename>) is copied or bind mounted into the
1366 <para>If set to
<literal>copy-uplink
</literal>,
<literal>replace-uplink
</literal> or
1367 <literal>bind-uplink
</literal> the uplink
<filename>resolv.conf
</filename> file managed by
1368 <filename>systemd-resolved.service
</filename> (specifically:
1369 <filename>/run/systemd/resolve/resolv.conf
</filename>) is copied or bind mounted into the
1372 <para>If set to
<literal>copy-stub
</literal>,
<literal>replace-stub
</literal> or
1373 <literal>bind-stub
</literal> the stub
<filename>resolv.conf
</filename> file managed by
1374 <filename>systemd-resolved.service
</filename> (specifically:
1375 <filename>/run/systemd/resolve/stub-resolv.conf
</filename>) is copied or bind mounted into the
1378 <para>If set to
<literal>delete
</literal> the
<filename>/etc/resolv.conf
</filename> file in the
1379 container is deleted if it exists.
</para>
1381 <para>Finally, if set to
<literal>auto
</literal> the file is left as it is if private networking is
1382 turned on (see
<option>--private-network
</option>). Otherwise, if
1383 <filename>systemd-resolved.service
</filename> is running its stub
<filename>resolv.conf
</filename>
1384 file is used, and if not the host's
<filename>/etc/resolv.conf
</filename> file. In the latter cases
1385 the file is copied if the image is writable, and bind mounted otherwise.
</para>
1387 <para>It's recommended to use
<literal>copy-…
</literal> or
<literal>replace-…
</literal> if the
1388 container shall be able to make changes to the DNS configuration on its own, deviating from the
1389 host's settings. Otherwise
<literal>bind
</literal> is preferable, as it means direct changes to
1390 <filename>/etc/resolv.conf
</filename> in the container are not allowed, as it is a read-only bind
1391 mount (but note that if the container has enough privileges, it might simply go ahead and unmount the
1392 bind mount anyway). Note that both if the file is bind mounted and if it is copied no further
1393 propagation of configuration is generally done after the one-time early initialization (this is
1394 because the file is usually updated through copying and renaming). Defaults to
1395 <literal>auto
</literal>.
</para>
1397 <xi:include href=
"version-info.xml" xpointer=
"v239"/></listitem>
1401 <term><option>--timezone=
</option></term>
1403 <listitem><para>Configures how
<filename>/etc/localtime
</filename> inside of the container
1404 (i.e. local timezone synchronization from host to container) shall be handled. Takes one of
1405 <literal>off
</literal>,
<literal>copy
</literal>,
<literal>bind
</literal>,
<literal>symlink
</literal>,
1406 <literal>delete
</literal> or
<literal>auto
</literal>. If set to
<literal>off
</literal> the
1407 <filename>/etc/localtime
</filename> file in the container is left as it is included in the image, and
1408 neither modified nor bind mounted over. If set to
<literal>copy
</literal> the
1409 <filename>/etc/localtime
</filename> file of the host is copied into the container. Similarly, if
1410 <literal>bind
</literal> is used, the file is bind mounted from the host into the container. If set to
1411 <literal>symlink
</literal>, a symlink is created pointing from
<filename>/etc/localtime
</filename> in
1412 the container to the timezone file in the container that matches the timezone setting on the host. If
1413 set to
<literal>delete
</literal>, the file in the container is deleted, should it exist. If set to
1414 <literal>auto
</literal> and the
<filename>/etc/localtime
</filename> file of the host is a symlink,
1415 then
<literal>symlink
</literal> mode is used, and
<literal>copy
</literal> otherwise, except if the
1416 image is read-only in which case
<literal>bind
</literal> is used instead. Defaults to
1417 <literal>auto
</literal>.
</para>
1419 <xi:include href=
"version-info.xml" xpointer=
"v239"/></listitem>
1423 <term><option>--link-journal=
</option></term>
1425 <listitem><para>Control whether the container's journal shall
1426 be made visible to the host system. If enabled, allows viewing
1427 the container's journal files from the host (but not vice
1428 versa). Takes one of
<literal>no
</literal>,
1429 <literal>host
</literal>,
<literal>try-host
</literal>,
1430 <literal>guest
</literal>,
<literal>try-guest
</literal>,
1431 <literal>auto
</literal>. If
<literal>no
</literal>, the journal
1432 is not linked. If
<literal>host
</literal>, the journal files
1433 are stored on the host file system (beneath
1434 <filename>/var/log/journal/
<replaceable>machine-id
</replaceable></filename>)
1435 and the subdirectory is bind-mounted into the container at the
1436 same location. If
<literal>guest
</literal>, the journal files
1437 are stored on the guest file system (beneath
1438 <filename>/var/log/journal/
<replaceable>machine-id
</replaceable></filename>)
1439 and the subdirectory is symlinked into the host at the same
1440 location.
<literal>try-host
</literal> and
1441 <literal>try-guest
</literal> do the same but do not fail if
1442 the host does not have persistent journaling enabled, or if
1443 the container is in the
<option>--ephemeral
</option> mode. If
1444 <literal>auto
</literal> (the default), and the right
1445 subdirectory of
<filename>/var/log/journal
</filename> exists,
1446 it will be bind mounted into the container. If the
1447 subdirectory does not exist, no linking is performed.
1448 Effectively, booting a container once with
1449 <literal>guest
</literal> or
<literal>host
</literal> will link
1450 the journal persistently if further on the default of
1451 <literal>auto
</literal> is used.
</para>
1453 <para>Note that
<option>--link-journal=try-guest
</option> is the default if the
1454 <filename>systemd-nspawn@.service
</filename> template unit file is used.
</para>
1456 <xi:include href=
"version-info.xml" xpointer=
"v187"/></listitem>
1460 <term><option>-j
</option></term>
1462 <listitem><para>Equivalent to
1463 <option>--link-journal=try-guest
</option>.
</para>
1465 <xi:include href=
"version-info.xml" xpointer=
"v187"/></listitem>
1470 </refsect2><refsect2>
1471 <title>Mount Options
</title>
1476 <term><option>--bind=
</option></term>
1477 <term><option>--bind-ro=
</option></term>
1479 <listitem><para>Bind mount a file or directory from the host into the container. Takes one of: a path
1480 argument — in which case the specified path will be mounted from the host to the same path in the container, or
1481 a colon-separated pair of paths — in which case the first specified path is the source in the host, and the
1482 second path is the destination in the container, or a colon-separated triple of source path, destination path
1483 and mount options. The source path may optionally be prefixed with a
<literal>+
</literal> character. If so, the
1484 source path is taken relative to the image's root directory. This permits setting up bind mounts within the
1485 container image. The source path may be specified as empty string, in which case a temporary directory below
1486 the host's
<filename>/var/tmp/
</filename> directory is used. It is automatically removed when the container is
1487 shut down. If the source path is not absolute, it is resolved relative to the current working directory.
1488 The
<option>--bind-ro=
</option> option creates read-only bind mounts. Backslash escapes are interpreted,
1489 so
<literal>\:
</literal> may be used to embed colons in either path. This option may be specified
1490 multiple times for creating multiple independent bind mount points.
</para>
1492 <para>Mount options are comma-separated.
<option>rbind
</option> and
<option>norbind
</option> control whether
1493 to create a recursive or a regular bind mount. Defaults to
<option>rbind
</option>.
<option>noidmap
</option>,
1494 <option>idmap
</option>,
<option>rootidmap
</option> and
<option>owneridmap
</option> control ID mapping.
</para>
1496 <para>Using
<option>idmap
</option>,
<option>rootidmap
</option> or
<option>owneridmap
</option> requires support
1497 by the source filesystem for user/group ID mapped mounts. Defaults to
<option>noidmap
</option>. With
1498 <option>x
</option> being the container's UID range offset,
<option>y
</option> being the length of the
1499 container's UID range, and
<option>p
</option> being the owner UID of the bind mount source inode on the host:
1502 <listitem><para>If
<option>noidmap
</option> is used, any user
<option>z
</option> in the range
1503 <option>0 … y
</option> seen from inside of the container is mapped to
<option>x + z
</option> in the
1504 <option>x … x + y
</option> range on the host. Other host users are mapped to
1505 <option>nobody
</option> inside the container.
</para></listitem>
1507 <listitem><para>If
<option>idmap
</option> is used, any user
<option>z
</option> in the UID range
1508 <option>0 … y
</option> as seen from inside the container is mapped to the same
<option>z
</option>
1509 in the same
<option>0 … y
</option> range on the host. Other host users are mapped to
1510 <option>nobody
</option> inside the container.
</para></listitem>
1512 <listitem><para>If
<option>rootidmap
</option> is used, the user
<option>0</option> seen from inside
1513 of the container is mapped to
<option>p
</option> on the host. Other host users are mapped to
1514 <option>nobody
</option> inside the container.
</para></listitem>
1516 <listitem><para>If
<option>owneridmap
</option> is used, the owner of the target directory inside of the
1517 container is mapped to
<option>p
</option> on the host. Other host users are mapped to
1518 <option>nobody
</option> inside the container.
</para></listitem>
1519 </itemizedlist></para>
1521 <para>Whichever ID mapping option is used, the same mapping will be used for users and groups IDs. If
1522 <option>rootidmap
</option> or
<option>owneridmap
</option> are used, the group owning the bind mounted directory
1523 will have no effect.
</para>
1525 <para>Note that when this option is used in combination with
<option>--private-users
</option>, the resulting
1526 mount points will be owned by the
<constant>nobody
</constant> user. That's because the mount and its files and
1527 directories continue to be owned by the relevant host users and groups, which do not exist in the container,
1528 and thus show up under the wildcard UID
65534 (nobody). If such bind mounts are created, it is recommended to
1529 make them read-only, using
<option>--bind-ro=
</option>. Alternatively you can use the
"idmap" mount option to
1530 map the filesystem IDs.
</para>
1532 <xi:include href=
"version-info.xml" xpointer=
"v198"/></listitem>
1536 <term><option>--bind-user=
</option></term>
1538 <listitem><para>Binds the home directory of the specified user on the host into the container. Takes
1539 the name of an existing user on the host as argument. May be used multiple times to bind multiple
1540 users into the container. This does three things:
</para>
1543 <listitem><para>The user's home directory is bind mounted from the host into
1544 <filename>/run/host/home/
</filename>.
</para></listitem>
1546 <listitem><para>An additional UID/GID mapping is added that maps the host user's UID/GID to a
1547 container UID/GID, allocated from the
60514…
60577 range.
</para></listitem>
1549 <listitem><para>A JSON user and group record is generated in
<filename>/run/userdb/
</filename> that
1550 describes the mapped user. It contains a minimized representation of the host's user record,
1551 adjusted to the UID/GID and home directory path assigned to the user in the container. The
1552 <citerefentry><refentrytitle>nss-systemd
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1553 glibc NSS module will pick up these records from there and make them available in the container's
1554 user/group databases.
</para></listitem>
1557 <para>The combination of the three operations above ensures that it is possible to log into the
1558 container using the same account information as on the host. The user is only mapped transiently,
1559 while the container is running, and the mapping itself does not result in persistent changes to the
1560 container (except maybe for log messages generated at login time, and similar). Note that in
1561 particular the UID/GID assignment in the container is not made persistently. If the user is mapped
1562 transiently, it is best to not allow the user to make persistent changes to the container. If the
1563 user leaves files or directories owned by the user, and those UIDs/GIDs are reused during later
1564 container invocations (possibly with a different
<option>--bind-user=
</option> mapping), those files
1565 and directories will be accessible to the
"new" user.
</para>
1567 <para>The user/group record mapping only works if the container contains systemd
249 or newer, with
1568 <command>nss-systemd
</command> properly configured in
<filename>nsswitch.conf
</filename>. See
1569 <citerefentry><refentrytitle>nss-systemd
</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
1572 <para>Note that the user record propagated from the host into the container will contain the UNIX
1573 password hash of the user, so that seamless logins in the container are possible. If the container is
1574 less trusted than the host it's hence important to use a strong UNIX password hash function
1575 (e.g. yescrypt or similar, with the
<literal>$y$
</literal> hash prefix).
</para>
1577 <para>When binding a user from the host into the container checks are executed to ensure that the
1578 username is not yet known in the container. Moreover, it is checked that the UID/GID allocated for it
1579 is not currently defined in the user/group databases of the container. Both checks directly access
1580 the container's
<filename>/etc/passwd
</filename> and
<filename>/etc/group
</filename>, and thus might
1581 not detect existing accounts in other databases.
</para>
1583 <para>This operation is only supported in combination with
1584 <option>--private-users=
</option>/
<option>-U
</option>.
</para>
1586 <xi:include href=
"version-info.xml" xpointer=
"v249"/></listitem>
1590 <term><option>--inaccessible=
</option></term>
1592 <listitem><para>Make the specified path inaccessible in the container. This over-mounts the specified path
1593 (which must exist in the container) with a file node of the same type that is empty and has the most
1594 restrictive access mode supported. This is an effective way to mask files, directories and other file system
1595 objects from the container payload. This option may be used more than once in case all specified paths are
1598 <xi:include href=
"version-info.xml" xpointer=
"v242"/></listitem>
1602 <term><option>--tmpfs=
</option></term>
1604 <listitem><para>Mount a tmpfs file system into the container. Takes a single absolute path argument that
1605 specifies where to mount the tmpfs instance to (in which case the directory access mode will be chosen as
0755,
1606 owned by root/root), or optionally a colon-separated pair of path and mount option string that is used for
1607 mounting (in which case the kernel default for access mode and owner will be chosen, unless otherwise
1608 specified). Backslash escapes are interpreted in the path, so
<literal>\:
</literal> may be used to embed colons
1611 <para>Note that this option cannot be used to replace the root file system of the container with a temporary
1612 file system. However, the
<option>--volatile=
</option> option described below provides similar
1613 functionality, with a focus on implementing stateless operating system images.
</para>
1615 <xi:include href=
"version-info.xml" xpointer=
"v214"/></listitem>
1619 <term><option>--overlay=
</option></term>
1620 <term><option>--overlay-ro=
</option></term>
1622 <listitem><para>Combine multiple directory trees into one overlay file system and mount it into the
1623 container. Takes a list of colon-separated paths to the directory trees to combine and the
1624 destination mount point.
</para>
1626 <para>Backslash escapes are interpreted in the paths, so
<literal>\:
</literal> may be used to embed
1627 colons in the paths.
</para>
1629 <para>If three or more paths are specified, then the last specified path is the destination mount
1630 point in the container, all paths specified before refer to directory trees on the host and are
1631 combined in the specified order into one overlay file system. The left-most path is hence the lowest
1632 directory tree, the second-to-last path the highest directory tree in the stacking order. If
1633 <option>--overlay-ro=
</option> is used instead of
<option>--overlay=
</option>, a read-only overlay
1634 file system is created. If a writable overlay file system is created, all changes made to it are
1635 written to the highest directory tree in the stacking order, i.e. the second-to-last specified.
1638 <para>If only two paths are specified, then the second specified path is used both as the top-level
1639 directory tree in the stacking order as seen from the host, as well as the mount point for the
1640 overlay file system in the container. At least two paths have to be specified.
</para>
1642 <para>The source paths may optionally be prefixed with
<literal>+
</literal> character. If so they are
1643 taken relative to the image's root directory. The uppermost source path may also be specified as an
1644 empty string, in which case a temporary directory below the host's
<filename>/var/tmp/
</filename> is
1645 used. The directory is removed automatically when the container is shut down. This behaviour is
1646 useful in order to make read-only container directories writable while the container is running. For
1647 example, use
<literal>--overlay=+/var::/var
</literal> in order to automatically overlay a writable
1648 temporary directory on a read-only
<filename>/var/
</filename> directory. If a source path is not
1649 absolute, it is resolved relative to the current working directory.
</para>
1651 <para>For details about overlay file systems, see
<ulink
1652 url=
"https://docs.kernel.org/filesystems/overlayfs.html">Overlay Filesystem
</ulink>.
1653 Note that the semantics of overlay file systems are substantially different from normal file systems,
1654 in particular regarding reported device and inode information. Device and inode information may
1655 change for a file while it is being written to, and processes might see out-of-date versions of files
1656 at times. Note that this switch automatically derives the
<literal>workdir=
</literal> mount option
1657 for the overlay file system from the top-level directory tree, making it a sibling of it. It is hence
1658 essential that the top-level directory tree is not a mount point itself (since the working directory
1659 must be on the same file system as the top-most directory tree). Also note that the
1660 <literal>lowerdir=
</literal> mount option receives the paths to stack in the opposite order of this
1663 <para>Note that this option cannot be used to replace the root file system of the container with an overlay
1664 file system. However, the
<option>--volatile=
</option> option described above provides similar functionality,
1665 with a focus on implementing stateless operating system images.
</para>
1667 <xi:include href=
"version-info.xml" xpointer=
"v220"/></listitem>
1673 <title>Input/Output Options
</title>
1677 <term><option>--console=
</option><replaceable>MODE
</replaceable></term>
1679 <listitem><para>Configures how to set up standard input, output and error output for the container
1680 payload, as well as the
<filename>/dev/console
</filename> device for the container. Takes one of
1681 <option>interactive
</option>,
<option>read-only
</option>,
<option>passive
</option>,
1682 <option>pipe
</option> or
<option>autopipe
</option>. If
<option>interactive
</option>, a pseudo-TTY is
1683 allocated and made available as
<filename>/dev/console
</filename> in the container. It is then
1684 bi-directionally connected to the standard input and output passed to
1685 <command>systemd-nspawn
</command>.
<option>read-only
</option> is similar but only the output of the
1686 container is propagated and no input from the caller is read. If
<option>passive
</option>, a pseudo
1687 TTY is allocated, but it is not connected anywhere. In
<option>pipe
</option> mode no pseudo TTY is
1688 allocated, but the standard input, output and error output file descriptors passed to
1689 <command>systemd-nspawn
</command> are passed on — as they are — to the container payload, see the
1690 following paragraph. Finally,
<option>autopipe
</option> mode operates like
1691 <option>interactive
</option> when
<command>systemd-nspawn
</command> is invoked on a terminal, and
1692 like
<option>pipe
</option> otherwise. Defaults to
<option>interactive
</option> if
1693 <command>systemd-nspawn
</command> is invoked from a terminal, and
<option>read-only
</option>
1696 <para>In
<option>pipe
</option> mode,
<filename>/dev/console
</filename> will not exist in the
1697 container. This means that the container payload generally cannot be a full init system as init
1698 systems tend to require
<filename>/dev/console
</filename> to be available. On the other hand, in this
1699 mode container invocations can be used within shell pipelines. This is because intermediary pseudo
1700 TTYs do not permit independent bidirectional propagation of the end-of-file (EOF) condition, which is
1701 necessary for shell pipelines to work correctly.
<emphasis>Note that the
<option>pipe
</option> mode
1702 should be used carefully
</emphasis>, as passing arbitrary file descriptors to less trusted container
1703 payloads might open up unwanted interfaces for access by the container payload. For example, if a
1704 passed file descriptor refers to a TTY of some form, APIs such as
<constant>TIOCSTI
</constant> may be
1705 used to synthesize input that might be used for escaping the container. Hence
<option>pipe
</option>
1706 mode should only be used if the payload is sufficiently trusted or when the standard
1707 input/output/error output file descriptors are known safe, for example pipes.
</para>
1709 <xi:include href=
"version-info.xml" xpointer=
"v242"/></listitem>
1713 <term><option>--pipe
</option></term>
1714 <term><option>-P
</option></term>
1716 <listitem><para>Equivalent to
<option>--console=pipe
</option>.
</para>
1718 <xi:include href=
"version-info.xml" xpointer=
"v242"/></listitem>
1722 <term><option>--background=
<replaceable>COLOR
</replaceable></option></term>
1724 <listitem><para>Change the terminal background color to the specified ANSI color as long as the
1725 container runs. The color specified should be an ANSI X3.64 SGR background color, i.e. strings such
1726 as
<literal>40</literal>,
<literal>41</literal>, …,
<literal>47</literal>,
<literal>48;
2;…
</literal>,
1727 <literal>48;
5;…
</literal>. See
<ulink
1728 url=
"https://en.wikipedia.org/wiki/ANSI_escape_code#SGR_(Select_Graphic_Rendition)_parameters">ANSI
1729 Escape Code (Wikipedia)
</ulink> for details. Assign an empty string to disable any coloring.
</para>
1731 <xi:include href=
"version-info.xml" xpointer=
"v256"/>
1739 <title>Credentials
</title>
1743 <term><option>--load-credential=
</option><replaceable>ID
</replaceable>:
<replaceable>PATH
</replaceable></term>
1744 <term><option>--set-credential=
</option><replaceable>ID
</replaceable>:
<replaceable>VALUE
</replaceable></term>
1746 <listitem><para>Pass a credential to the container. These two options correspond to the
1747 <varname>LoadCredential=
</varname> and
<varname>SetCredential=
</varname> settings in unit files. See
1748 <citerefentry><refentrytitle>systemd.exec
</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
1749 details about these concepts, as well as the syntax of the option's arguments.
</para>
1751 <para>Note: when
<command>systemd-nspawn
</command> runs as systemd system service it can propagate
1752 the credentials it received via
<varname>LoadCredential=
</varname>/
<varname>SetCredential=
</varname>
1753 to the container payload. A systemd service manager running as PID
1 in the container can further
1754 propagate them to the services it itself starts. It is thus possible to easily propagate credentials
1755 from a parent service manager to a container manager service and from there into its payload. This
1756 can even be done recursively.
</para>
1758 <para>In order to embed binary data into the credential data for
<option>--set-credential=
</option>,
1759 use C-style escaping (i.e.
<literal>\n
</literal> to embed a newline, or
<literal>\x00
</literal> to
1760 embed a
<constant>NUL
</constant> byte). Note that the invoking shell might already apply unescaping
1761 once, hence this might require double escaping!.
</para>
1764 <citerefentry><refentrytitle>systemd-sysusers.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1766 <citerefentry><refentrytitle>systemd-firstboot
</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1767 services read credentials configured this way for the purpose of configuring the container's root
1768 user's password and shell, as well as system locale, keymap and timezone during the first boot
1769 process of the container. This is particularly useful in combination with
1770 <option>--volatile=yes
</option> where every single boot appears as first boot, since configuration
1771 applied to
<filename>/etc/
</filename> is lost on container reboot cycles. See the respective man
1772 pages for details. Example:
</para>
1774 <programlisting># systemd-nspawn -i image.raw \
1776 --set-credential=firstboot.locale:de_DE.UTF-
8 \
1777 --set-credential=passwd.hashed-password.root:'$y$j9T$yAuRJu1o5HioZAGDYPU5d.$F64ni6J2y2nNQve90M/p0ZP0ECP/qqzipNyaY9fjGpC' \
1780 <para>The above command line will invoke the specified image file
<filename>image.raw
</filename> in
1781 volatile mode, i.e. with empty
<filename>/etc/
</filename> and
<filename>/var/
</filename>. The
1782 container payload will recognize this as a first boot, and will invoke
1783 <filename>systemd-firstboot.service
</filename>, which then reads the two passed credentials to
1784 configure the system's initial locale and root password.
</para>
1786 <xi:include href=
"version-info.xml" xpointer=
"v247"/>
1791 </refsect2><refsect2>
1792 <title>Other
</title>
1795 <xi:include href=
"standard-options.xml" xpointer=
"no-pager" />
1796 <xi:include href=
"standard-options.xml" xpointer=
"help" />
1797 <xi:include href=
"standard-options.xml" xpointer=
"version" />
1802 <xi:include href=
"common-variables.xml" />
1805 <title>Examples
</title>
1809 <ulink url=
"https://getfedora.org">Fedora
</ulink> image and start a shell in it
</title>
1811 <programlisting># machinectl pull-raw --verify=no \
1812 https://download.fedoraproject.org/pub/fedora/linux/releases/
&fedora_latest_version;/Cloud/x86_64/images/Fedora-Cloud-Base-
&fedora_latest_version;-
&fedora_cloud_release;.x86_64.raw.xz \
1813 Fedora-Cloud-Base-
&fedora_latest_version;-
&fedora_cloud_release;.x86-
64
1814 # systemd-nspawn -M Fedora-Cloud-Base-
&fedora_latest_version;-
&fedora_cloud_release;.x86-
64</programlisting>
1816 <para>This downloads an image using
1817 <citerefentry><refentrytitle>machinectl
</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1818 and opens a shell in it.
</para>
1822 <title>Build and boot a minimal Fedora distribution in a container
</title>
1824 <programlisting># dnf -y --releasever=
&fedora_latest_version; --installroot=/var/lib/machines/f
&fedora_latest_version; \
1825 --repo=fedora --repo=updates --setopt=install_weak_deps=False install \
1826 passwd dnf fedora-release vim-minimal util-linux systemd systemd-networkd
1827 # systemd-nspawn -bD /var/lib/machines/f
&fedora_latest_version;</programlisting>
1829 <para>This installs a minimal Fedora distribution into the
1830 directory
<filename index=
"false">/var/lib/machines/f
&fedora_latest_version;</filename>
1831 and then boots that OS in a namespace container. Because the installation
1832 is located underneath the standard
<filename>/var/lib/machines/
</filename>
1833 directory, it is also possible to start the machine using
1834 <command>systemd-nspawn -M f
&fedora_latest_version;</command>.
</para>
1838 <title>Spawn a shell in a container of a minimal Debian unstable distribution
</title>
1840 <programlisting># debootstrap unstable ~/debian-tree/
1841 # systemd-nspawn -D ~/debian-tree/
</programlisting>
1843 <para>This installs a minimal Debian unstable distribution into
1844 the directory
<filename>~/debian-tree/
</filename> and then
1845 spawns a shell from this image in a namespace container.
</para>
1847 <para><command>debootstrap
</command> supports
1848 <ulink url=
"https://www.debian.org">Debian
</ulink>,
1849 <ulink url=
"https://www.ubuntu.com">Ubuntu
</ulink>,
1850 and
<ulink url=
"https://www.tanglu.org">Tanglu
</ulink>
1851 out of the box, so the same command can be used to install any of those. For other
1852 distributions from the Debian family, a mirror has to be specified, see
1853 <citerefentry project='die-net'
><refentrytitle>debootstrap
</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
1858 <title>Boot a minimal
1859 <ulink url=
"https://www.archlinux.org">Arch Linux
</ulink> distribution in a container
</title>
1861 <programlisting># pacstrap -c ~/arch-tree/ base
1862 # systemd-nspawn -bD ~/arch-tree/
</programlisting>
1864 <para>This installs a minimal Arch Linux distribution into the
1865 directory
<filename>~/arch-tree/
</filename> and then boots an OS
1866 in a namespace container in it.
</para>
1871 <ulink url=
"https://software.opensuse.org/distributions/tumbleweed">OpenSUSE Tumbleweed
</ulink>
1872 rolling distribution
</title>
1874 <programlisting># zypper --root=/var/lib/machines/tumbleweed ar -c \
1875 https://download.opensuse.org/tumbleweed/repo/oss tumbleweed
1876 # zypper --root=/var/lib/machines/tumbleweed refresh
1877 # zypper --root=/var/lib/machines/tumbleweed install --no-recommends \
1878 systemd shadow zypper openSUSE-release vim
1879 # systemd-nspawn -M tumbleweed passwd root
1880 # systemd-nspawn -M tumbleweed -b
</programlisting>
1884 <title>Boot into an ephemeral snapshot of the host system
</title>
1886 <programlisting># systemd-nspawn -D / -xb
</programlisting>
1888 <para>This runs a copy of the host system in a snapshot which is removed immediately when the container
1889 exits. All file system changes made during runtime will be lost on shutdown, hence.
</para>
1893 <title>Run a container with SELinux sandbox security contexts
</title>
1895 <programlisting># chcon system_u:object_r:svirt_sandbox_file_t:s0:c0,c1 -R /srv/container
1896 # systemd-nspawn -L system_u:object_r:svirt_sandbox_file_t:s0:c0,c1 \
1897 -Z system_u:system_r:svirt_lxc_net_t:s0:c0,c1 -D /srv/container /bin/sh
</programlisting>
1901 <title>Run a container with an OSTree deployment
</title>
1903 <programlisting># systemd-nspawn -b -i ~/image.raw \
1904 --pivot-root=/ostree/deploy/$OS/deploy/$CHECKSUM:/sysroot \
1905 --bind=+/sysroot/ostree/deploy/$OS/var:/var
</programlisting>
1910 <title>Exit status
</title>
1912 <para>The exit code of the program executed in the container is
1917 <title>See Also
</title>
1918 <para><simplelist type=
"inline">
1919 <member><citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
1920 <member><citerefentry><refentrytitle>systemd.nspawn
</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
1921 <member><citerefentry project='man-pages'
><refentrytitle>chroot
</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
1922 <member><citerefentry project='mankier'
><refentrytitle>dnf
</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
1923 <member><citerefentry project='die-net'
><refentrytitle>debootstrap
</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
1924 <member><citerefentry project='archlinux'
><refentrytitle>pacman
</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
1925 <member><citerefentry project='mankier'
><refentrytitle>zypper
</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
1926 <member><citerefentry><refentrytitle>systemd.slice
</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
1927 <member><citerefentry><refentrytitle>machinectl
</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
1928 <member><citerefentry project='url'
><refentrytitle url='https://btrfs.readthedocs.io/en/latest/btrfs.html'
>btrfs
</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
1929 </simplelist></para>